Wireless mesh networks are becoming important. In a mesh network, routing tables can become rather large, and there is incentive to have routing be carried out at layer-2 as much as possible. For this reason, a six-address scheme is being considered for mesh networks by the IEEE 802.11 standards committee. Such a six-address scheme permits tunneling between a mesh access point and a mesh client of a mesh access point, and between two mesh clients using a single MAC header, proposed to be an IEEE 802.11s header, which is an extension of the an IEEE 802,11 MAC header. However, dealing with such 6-address methods may require new hardware that can handle such 6-address formats. There is still room for alternate methods for layer-2 routing in a wireless mesh network.
In general networks, e.g., wired networks, “label switching,” also called “tag switching” is known. One example is Multi-Protocol Label Switching (MPLS). Routing can be thought of as determining the forwarding equivalence class of a packet, and then assigning a route for that forwarding equivalence class of packets. In MPLS, the assignment of a particular packet to a particular forwarding equivalence class is done once as the packet enters the network. The forwarding equivalence class to which the packet is assigned is encoded as a short fixed length value known as a “label” or “tag”. Routers determine paths to a next router for each forwarding equivalent class. A label can be used to represent the route. When a packet is forwarded to its next hop, the label is sent along with it; that is, the packets are “tagged” before they are forwarded. At subsequent hops, there is no further analysis of the packet's network layer header. Rather, the label is used as an index into a table which specifies the next hop, and a new label. The old label is replaced with the new label, and the packet is forwarded to its next hop. In MPLS, Multiple routers assign different labels. As the route represented by a label is followed, when a packet arrives at some intermediate point, if the route to the ultimate destination corresponds to a previously labeled route, label switching (swapping of labels) occurs and the packet is forwarded along to the next hop of the new label in the packet. MPLS forwarding can be done by switches which are capable of doing label lookup and replacement, but need not be capable of analyzing the network layer headers.
MPLS may be difficult to apply to a wireless mesh network. When a mesh packet arrives at some intermediate point in the mesh, using a previously assigned path and the tag thereof and swapping the tag of the packet requires all intermediate points to be constantly updated of the status of all paths. The status of various links in a mesh network changes frequently, and therefore, making sure all intermediate points are updated would lead to a lot of control information being maintained at the intermediate points, and being exchanged throughout the mesh network.
Mesh networks may be centrally controlled in that each mesh point is a lightweight wireless device with much of its functionality controlled by a centralized controller. In such a mesh network, there is advantage to centralized routing compared to local distributed routing by the mesh points. For example, centralized routing can provide a route between two mesh points without having to route via the root mesh point.